Radio bomb release system



am 4, w49. R. c. SANDERS, JR., Erm.. 2,458,429

RADIO BOMB RELEASE SYSTEM l 2 Sheets-Sheet l Filed July 1s, 1945 jan. 4, H949. R. c. SANDERS, JR., ETAL RADIO BOMB RELEASE SYSTEM Filed July 16, 1945 INVE T0125 #7M/WJ?? `Patented Jan. 4, i949 f carica assenza mimo sormanmnsa srs'rain Ware Application .luly 16, 1945, Serial No. tl

This invention relates to radio bomb release systems, and more particularly to improvements in systems of the type described in copending U. S. application Serial No. 524,794, led March 2, 1 944 by Royden C. Sanders, Jr., and William R. Mercer, and entitled Radio bomb release system, which issued December 17, 1946, as Patent No. 2,412,632.

The principal object of the present invention is to provide a system of the described type including means for automatically compensating the eiects of altitude so as to provide correct operation at Iany altitude within' a predetermined range.

The invention will be described with reference to the accompanying drawings wherein:

Figure 1 is a diagram showing the geometry of a bomb release problem, i

Figure 2 is a graph showing the relationship of slant range to slant` speed for bomb release at a particular altitude, and the linear approximation to said relationship,

Figure 3 is a schematic circuit diagram of a radio bomb release system embodying the present invention,

vFigure 4 is a graph illustrating the variations in frequency of the signals transmitted and received in the operation of the system of Figure 3, and v f Figure. 5 is a graph illustrating the variations in frequency of the beat signal produced in the operation of the system of Figure 3.

Refer to Figure l. It is `assumed that an aircraft at the point P is ilying horizontally at a velocity G toward a point M, directly over a. target at the point Q, at an altitude'H. A bomb released at the altitude H without any vertical elapse before the craft reaches the point M is If the horizontal speed G and thehorizontal component D of the target; range were known,

the calculation of T would be a simple matter.

5 Claims. (Cl. 343-?) 30 isfied for proper release.

The condition for release is: T=Tf, or substitut- V ing (i) and (2),

`D 2H (3) n g Radio reiiection equipment does not'measure the horizontal distance D, but the true or slant distance R. Similarly, the horizontal speed G is not measured directly, but its slant. component S is measured. Accordingly, itis necessary to determine the time 'If in terms of these quantities. It is apparent from Figure 1 that at great distances or low altitudes from the target, the target the distance is decreased or the altitude increased, the differences between the slant and horizontal speeds and distances will increase.

Referring to Figure 2, the curveV l shows the relation between slant speed S and slant range R which corresponds to one particular value of Tl,

which in turn is the time of fall Tf from an altitude H1. Thus if a bomb is released from the altitude H1, when R, and S are of such values as to satisfy the relationship represented by the curve I, the bomb will strike the target.

For every different altitude, there is a different relationship between R and S which must be sat- The curve l is thus but one of a family of similar curves. In the present system a linear approximation is used, rather than the actual Rf-S relationship. This approximation need be accurate vonly within the range S' to S" of slant speeds whichwill occur speeds from S" to S'.

The equation of the line 3 is (4) R=mS+Ro where m is the slope of the line:

and Bn is the range intercept at zero speed, as indicated in Figure 2. As stated above', the relations shown in Figure 2 correspond to one specied altitude, H1. For any other altitude, both m and Ro will have .correspondingly diilerent values. By settingin the values of mand Ro corresponding to theparticular altitude H at which a craft ls-iiying, a substantially correct 1' )lease may be obtained by satisfying the rela.- tionship of Equation 4.

Refer to Figure 3. A radio transmitter 5 is provided with an antenna 1, and is connected to a. frequency modulator 9, which may be of the type described in copending U. S. patent application Serial No. 471,003, filed January 1, 1943, by S. V. Perry, and entitled Capacity modulator unit, or any other known device for varying the frequency of operation of the transmitter 5 in accordance with the voltage applied to it. In the present illustration, the modulator 9 is energized in such manner as to provide triangular wave frequency modulation of the transmitter l.

A D.C. source Il is connected across resistors I3, I5 and I1. An adjustable resistor 25 is connected across the resistor I5. A switch I9 `1s connected across the resistor I1, and is arranged to be cyclically opened and closed by a cam 2|, continuously driven by a motor 23. This periodically changes the voltage at the junction point I4 of resistors I3 and I5 between two values which differ by an amount depending upon the setting of the resistor 25.

The point I4 is connected to a wave shaping circuit 21. The circuit 21 may be merely an integrating circuit, or may be of the type described in copending U. S. patent application Serial No. 546,537, filed July 25, 1944, by Royden C. Sanders, Jr., and entitled Wave shapingcircuits, which issued Ju1y9, 1946, as Patent No. 2,403,616. The circuit 21 converts the square Wave voltage input from the point I4 vto a substantially triangular wave voltage, which is applied to the modulator 9. A resistor 29 is included in the input circuit of the wave shaping circuit 21. By adjusting the resistor 25, the band width through which the frequency of the transmitter 5 is swept may be varied.

A receiver 3l is provided with an antenna 33, and is also coupled to the transmitter 5 through a transmission line 35. An amplitude limiter 31 is connected to the output of the receiver 3 I. The output circuit of the limiter 31 is connected to a pair of frequency responsive circuits comprising' averaging cycle counters 39 and 4I respectively. The counter 39 includes a capacitor 43, connected from the limiter 31 to the anode of a rtriode 45 and to the cathode of a diode 41. The cathode of the triode 45 is connected to the control grid of an amplifier tube 49. The entire load resist'- ance 5I associated with the tube 49 is connected in its cathode circuit so that it acts as a so-called cathode follower. The anode of the diode 41 is connected to a tap 53 on the resistor 5I.

The counter 4I includes a capacitor 55 connected from the limiter 31 to the anode of a triode 51 and to the cathode 0f a diode 59. The anode of the diode 59 is connected to the control grid of the cathode follower tube 49. The cathode of the triode 51 is connected to the. upper end of the load resistor 5I, at the cathode of the tube l49. The counters 39 and 4I are provided with a common storage capacitor 6I, connected between the control grid of the tube 49 and ground. They also have a common load resistor 63, connected from the grid of the tube 49 to a point 65 on a voltage divider chain described hereinafter.

The control grid of the triode 45 of the counter 39 is coupled to' the ungrounded end of the resistor I1. so that a square wave voltage is applied thereto in synchronsm with the frequency modulation of the transmitter 5. The control grid of the triode 51 is coupled to the same point through a phase inverter 61, so that the square wave voltage applied thereto is out of phase with that at the grid of the triode 45. such that the triode 51 is cut olf and the triode 45 is conductive while the frequency of the transmitter 5 is increasing, and the triode 45 is cut oil and the triode 51 is conductive while the transmitted frequency is decreasing.

The cathode of the cathode follower tube 49 is connected to the cathode of a relay amplifier tube 69. The anode circuit of the tube 69 includes the actuating coil of a relay 1 I. The contacts of the relay 1I are connected to the actuating circuit of a bomb release -mechanism (not shown). The control grid of the relay tube 69 is by-passed to the cathode through a capacitor I13, and is connected through a resistor 15 to the adjustable contact ofa variable voltage divider 11.

The voltage divider 11 is shunted across a portion of a voltage divider chain including xed resistors 19, 8|, 83, and 85and variable resistors 81 and 89, serially connected across the D.C. source Il. The voltages at the terminals of the voltage divider 11 are controlled by the variable resistors 81 and 89, and the potential at the control grid of the relay tube 69 is Variable between these two voltages by adjustment of the voltage divider 11'. The return point 65 of the counter load resistor 63 is the junction between the fixed resistors 83 and 85.

The adjustment and operation of the system thus far described is as follows:

Owing to the cyclical operationv of the switch I9 by the motor 23, the frequency of the output of the transmitter 5 varies cyclically as shown by the solid line IUI of Figure 4. Some of this output is transferred directly to the receiver 3| through the line 35. The greater portion is radiated by the antenna 1. Some of the radiated energy strikes the selected target (not shown), and is reflectedto the antenna 33. The time required for the transmitted energy to travel to the target and back to the vantenna 33 is proportional to the slant range R from the aircraft to the target. The variations in frequency of the received energy are accordingly delayed with respect to those of the transmitted energy. The variation of frequency of the received signal as a function of time, assuming no relative motion between the aircraft and the target, is shown by the dot line |03. The delay Tr is proportional to the range R.

Now if the range is decreasing at a rate S, the frequency of the received signal will be increased, owing to doppler effect. Thus the frequency of the received signal will vary with time as shown by the dash line |05. The increase in frequency Fs is directly proportional to the speed S.

The direct and reflected signals from the transmitter 5 areimixed and detected in the receiver 3|. The output of the receiver comprises a beat frequency signal, which has a frequency equal to the difference in the frequencies of the two signals applied to the receiver. The frequency of this beat signal varies with time as shown by the solid line graph |06 of Figure 5. The mean value of the beat frequency, indicated by lthe dash line I01 in Figure 5, is directly proportional to the range R, and is equal to:

6 fait The connections are' feet. The beat frequency varies cyclically above and below its mean value by the amount Fs. During increase of transmitter frequency the beat where .fo is the mean transmitted frequency (see Figure 4) in cycles per second, S in the slant speed in feet per second, and c is the velocity of wave propagation (the velocity of light) in feet per second. During decrease of transmitter frequency the beat frequency is:

As mentioned above, the triode 51 of the counter il! is cut off during increase of transmitted frequency, and the triode 135 of the counter 39 is conductive. During this period, the counter 39 operates to provide an average current iu in the direction of the solid arrow through the load resistor 63. This current is:

where k1 is a constant directly proportional to the capacitance of the capacitor Q3. The counter di does not operate.

During decrease of transmitted frequency, the triode d5 is cut oi and the counter -39 does not operate. The triode '51 is conductive, and the counter 13| provides an average current id in the direction of the dash arrow through the load resistor 53. This current is:

a=k.fd,=k2(fg{R where k2 is a constant directly proportional to f the capacitance of the capacitor 55. The common load capacitor 6| averages the pulsations in the voltage at the control grid of the cathode follower tube 49, so that the voltage between the cathode follower grid and ground is (11) ewig-11a "lfR e al? (f..f.R 2fS k (f MSH where eo is the potential at theA point 65 and RL is the resistance of the load resistor 63.

The cathode of the tube 49 is maintained at substantially the same potential as the control grid as long as the current through the resistor 5l is only the anode current of the tube t9. 'Ihus the potential at the cathode of the relay tube 69 is the same as that at the grid of the tube 49. The potential at the control grid of the relay tube (referred to ground) is the voltage e1 at the tap of the voltage divider 11. Thus the voltage es between the cathode and the control grid of the relay tube is:

Rearranging the terms,

The quantities k1, k2, RL, ,im and fo are all constants, determined in accordance with design considerations. Therefore Equation 12 can be written as:

tube 69 starts to conduct, the relay 1l is closed.

At this time l 6'8"-80-91-i-K1flR- K25 The slant range is therefore:

in accordance with the altitude H, the relay can be made to operate at the proper release time, within the limits of the linear approximationof the corresponding R-S curve. l

It is apparent from Equation 15 that m is inversely proportional to the band Width ,f. Accordingly, the proper value of m for any particular altitude H may be obtained by adjustment of the sweep width control 25. Ro, as shown by Equation 16, is also inversely proportional to the band width, and is directly proportional to the voltage which must be present' across-the counter load resistor 63 to cause the relay tube 69 to conduct. This voltage is the diierence between the total :bias from cathode to grid of the relay tube 69, (eo-e1), and` the cutoif bias e's, and is a function ofthe settings of the variable resistors 89, 81 and 11, whichcontrol the bias e1 at the grid of the relay tube 69. The variable resistor 89 is employed to control Ro in accordance withV the altitude.

The variable resistor A11 is provided to allow variation of the bias e1 on the relay tube for the purpose of obtaining an adjustable range lead,

so that release may be made to occur a certain distance in advance of the target. Since the voltage required for a given range lead will vary with altitude, the variable resistor 81 is included .to set the voltage across the resistor 11 as a function of altitude. Thusa given setting of the resistor 11 will provide a given range lead, regardless of the altitude.

The controls 81, 89 and 25 are ganged on a shaft H0 inv order that the modulation band width and the bias voltages may be adjusted simultaneously to correspond with the altitude. None of these quantities are linear functions of 'the altitude. The resistors 81 and 89 are designed with resistance-rotation characteristics comprising two linear portions of different slopes to provide approximately the required variations of voltage with rotation of the shaft ||0.

are negligible.

The modulation band width must be held within about one percent of the correct value. While this could be achieved with a tapered variable resistor, there would be difficulty in constructing such a device, and it would necessarily be large in order to obtain the required accuracy. On the other hand, it is relatively easy to make a variable resistor of reasonable size having an accurately linear resistance-rotation characteristic..

By proper proportioning of the resistors I3, I5, Il and 29, the variable resistor 25 may be made linear and yet provide the correct characteristic of band width vs. shaft position.

The shaft IIIl may be set manually to a position corresponding to the altitude at which a Practically, the errors introduced by this arrangement to a bias source comprising an adjustable voltage divider IIS connected in series with a resistor |2I across the source II. This bias is applied to the tube III through a resistor |23.

The resistor |23 comprises the load resistor for a counter circuit |25. The counter |25 is connected to the output circuit of an amplitude limiter |21, which in turn is connected to the out put circuit of a receiver |29. A transmitter I3l, including means for cyclically varying the transmitted frequency, is coupled to the receiver |29 and is provided with an antenna |33. A similar antenna is connected to the receiver |29.

The counter |25, limiter |21, receiver |29, and transmitter I3I comprise a radio reflection altimeter, and cooperate in known manner to provide a voltage across the load resistor |23 bearing a predetermined relationship to the altitude H, and in opposing polarity to the bias voltage provided by the voltage divider II9. When the algebraic sum of this voltage and the voltage at the adjustable tap of the voltage divider I I9 is negative with respect to the cutoff voltage of the relay tube I|'|, the relay I|3 is deenergized. This connects the motor tothe source I I5 in such polarity as to rotate the shaft |Ill' in the direction corresponding to increase of altitude. The tap of the voltage divider is rotated to produce more positive bias, until the voltage across the counter load resistor is neutralized. The relay tube I'I'I starts to conduct, energizing the relay II3 and disconnecting the motor III from its source |I5.

The relay I I3 is provided with a small dead space so that a slight increase of energization is required to close the upper contacts. Thus if the voltage across the counter load resistor |23 decreases, the relay will operate to its upper position, energizing the motor I|I to rotate the shaft I I0 in the direction corresponding to decrease of altitude. Thus the shaft H0 is maintained substantially continuously at a position corresponding to the altitude.

The invention has been described as an improved bomb release system of the radio reflection type wherein signals radiated from an aircraft tov a selected target are picked up after reflection thereby, and utilized to provide slant range and slant speed information. The altitude is measured continuously by a radio reflection altimeter, which controls a servo system. The servo system operates control devices to modify the range and speed information as functions of the altitude. The modified range and speed information is employed to effect release of a bomb.

We claim as our invention:

1. In a radio bomb release system which includes radio reflection means substantially continuously responsive to the slant distance and slant speed of an aircraft with 'respect to a selected target to provide an output comprising two differentially related components which are predetermined functions respectively of said distance and said speed,and relay means responsive to the attainment by said output of a predetermined magnitude to effect release of a bomb, altimeter means substantially continuously responsive to the altitude of said craft to provide an output corresponding in magnitude to said altitude means responsive to the output of said altimeter to control the response sensitivity of said radio reflection means t'o distance as a predetermined function of said altitude, and means responsive to the output of said altimeter to bias said relay means in accordance with a predetermined function of said altitude.

2. In a radio bomb release system including frequency modulated transmitter means, a receiver, counter meansJdifferentially responsive to the output of said receiver during increase and decrease respectively of the frequency of operation ofA said transmitter, and relay means responsive to the output of said counter means to effect release of a bomb upon the attainment of a predetermined magnitude by said output of said counter means, an altimeter, means responsive to said altimeter to control the modulation band width of said transmitter means, means for -applying a bias to said relay means, and means responsive to said altimeter to control the magnitude of said bias.

3. In a radio reflection system of the decribed type, including a radio transmitter and modulator means connected thereto to vary the frequency of operation thereof, a source of cyclically varying modulation voltage, comprising a direct current source, a chain of series connected resistors connected across said direct current source, a periodic switch connected across one of the resistors of said chain, and a variable resistor connected acrpss another of the resistors predetermined function of the relationship be tween said distance and said speed, and relay means responsive to the attainment by said output of a predetermined magnitude to effect release of a bomb, altimeter means substantially continuously responsive to the `altitude of said craft to provide an output corresponding in magnitude to saidaltitude, means responsive to the output of said'f altimeter to control .the response sensitivity offs'aid radio reflection means to distance as a .predetermined function of said altitude, and means responsive to the output of said altimeter to bias said relay means in accordance with a predetermined function of said altitude.

5. In a radivbomb release system including frequency modulated transmitter means, a receiver,

means differentially responsive to the frequency i of the outputof said receiver duringr increase and decrease respectively of the frequency of operation of said transmitter, and relay means rel5 sponsive to the output of said frequency responsive means to effect release of a bomb upon the attainment of a predetermined magnitude by said output of said frequency responsive means, an altimeter, and means responsive to said altimeter to control the modulation band width of said transmitter means, means for applying a bias to said relay means, and means responsive to said altimeter to control the magnitude of l0 said bias.

ROYDEN C. SANDERS,V JR. DANIEL BLITZ.

No references cited. 

